1. Field of the Invention
The present invention relates to a fuel cell, more particularly relates to a single chamber fuel cell in which a cell is placed in a mixed fuel gas comprised of hydrogen or another fuel gas and oxygen.
2. Description of the Related Art
Science, vol. 288 (2000), p. 2031–2033, Journal of The Electrochemical Society, 149 (2) A133–A136 (2002), etc. propose a single chamber fuel cell shown in FIG. 5. The single chamber fuel cell shown in FIG. 5 consists of a cell 106, comprised of a solid electrolyte layer 100 on the two sides of which a cathode layer 102 and anode layer 104 are formed, placed in a chamber 110 supplied with a mixed fuel gas of a fuel gas and oxygen or an oxygen-containing gas through a feed pipe 108. The drive temperature of the fuel cell is about 500 to 600° C. The gas in the chamber 110 is exhausted outside of the system through an exhaust pipe 112.
According to the single chamber fuel cell shown in FIG. 5, by placing the cell 106 in a mixed fuel gas, it is possible to place the entire cell 106 in substantially the same atmosphere. Therefore, the cell 106 can be improved in durability compared with a double chamber fuel cell exposing the two sides of the cell to different atmospheres.
In the single chamber fuel cell shown in FIG. 5, power is generated in the following way. That is, the oxygen (O2) at the cathode layer 102 side of the cell 106 is ionized to oxygen ions (O2−) at the boundary of the cathode layer 102 and the solid electrolyte layer 100 comprised of YSZ or another solid electrolyte. The oxygen ions (O2−) are conducted to the anode layer 104 by the solid electrolyte layer 100. The oxygen ions (O2−) conducted to the anode layer 104 react with methane (CH4) or another fuel gas supplied to the anode layer 104 whereby water (H2O), carbon dioxide (CO2), hydrogen (H2), and carbon monoxide (CO) are produced. During this reaction, the oxygen ions discharge electrons, so a potential difference arises between the cathode layer 102 and anode layer 104. Therefore, by electrically connecting the cathode layer 102 and anode layer 104 by a takeout line 114, the electrons of the anode layer 104 flow through the takeout line 114 in the direction of the cathode layer 102 (arrow direction) and electricity can be taken out from the fuel cell.
In the single chamber fuel cell shown in FIG. 5, however, the reaction at the cathode layer 102 side and the reaction at the anode layer 104 side are believed to occur simultaneously mixed without differentiation between the cathode layer 102 side and the anode layer 104 side. Therefore, for example, sometimes the oxygen ions (O2−) produced at the cathode layer 102 side of the solid electrolyte layer 100 react with the methane (CH4) or other fuel gas (oxidation reaction) present even at the cathode layer 102 side. In this case, electrons are transferred only at the cathode layer 102 side, no potential difference arises between the cathode layer 102 and anode layer 104, and electrical energy cannot be taken out. Therefore, in a single chamber fuel cell, the power generation efficiency is liable to drop.
Further, the oxygen ions produced at the boundary of the cathode layer 102 and solid electrolyte layer 100 are conducted through the solid electrolyte layer 100 and move to the anode layer 104 side. Therefore, a large resistance acts in the conduction of oxygen ions through the solid electrolyte layer 100. From this viewpoint as well, in a single chamber fuel cell, the power generation efficiency is liable to drop.